This invention relates to a gauge which can be used to determine the proper sunscreen lotion to apply to one's skin on any given day to prevent harmful UV radiation from reaching the skin. Alternately, a gauge is disclosed which will signal the user that applied sunscreen lotion is depleted, either through evaporation, bathing, etc., to the extent that it no longer provides protection and more lotion should be applied.
Exposure to sunlight and its UV-B component can result in four distinct skin damage conditions: sunburn; pigmentary and texture changes in the skin; actinic damage or sking aging; and development of nonmelanoma skin cancer and malignant melanoma skin cancer.
The relationship between UV exposure and the cause and risk of these skin damage conditions has been quantified (Fears TR, Scotto J: Estimating increases in skin cancer morbidity due to increases in ultraviolet radiation exposure. Cancer Invest, 1983; 1:119-126).
Other studies have classified the UV-B spectrum (frequencies from 290 nanometers to 330 nanometers) as the prime cause of sunburn (Nachtwey DS, Rundel RD: A photobiological evaluation of tanning booths. Science, 1981; 211:405-407). Because UV-B is a mutagen (Suzuki F, Han A, Lankas GR, et al: Spectral dependencies of killing, mutation, and transformation in mammalian cells and their relevance to hazards caused by solar ultraviolet radiation. Cancer Research, 1982; 41:4916-4924 and Doniger J, Jacobsen ED, Krell K, et al: Ultraviolet light action spectra for neoplastic transformation and lethality of Syrian hamster embryo cells correlate with spectra for pyrimidine dimer formation in cellular DNA. Proc National Academy of Science USA, 1981; 78:2378-2382), the risk of nonmelanoma skin cancer and malignant melanoma is a cumulative and long lasting medical danger to a large number of the World's population (Robert S. Stern, M.D., Milton C. Weinstein, Ph.D., Stuart G. Baker, ScD: Risk reduction for nonmelanoma skin cancer with childhood sunscreen use, Arch Dermatol, 1986; 122:537-545).
A variety of colorless sunscreen lotions that can block most UV-B from penetrating the epidermis layer of the skin and prevent these dangerous medical conditions have been developed and are marketed commercially. The effectiveness of these sunscreens in reducing sunburn in humans is well established (Cripps DJ, Hegedus S: Protection factor of sunscreens to monochromatic radiation, Arch Dermatol, 1974; 109:202-204).
A grading system called the "sun protective factor" (SPF) is used to quantify the degree of protection afforded by a given sunscreen lotion (Pathak MA: Sunscreens: Topical and systemic approaches for protection of human skin against harmful effects of solar radiation, Journal of American Acad Dermatol, 1982; 7:285-312).
The SPF number is the ratio of the dose of UV radiation required to produce minimal pinkness 24 hours after exposure on skin covered by the sunscreen, to the dose of UV radiation required to produce similar pinkness on unprotected skin.
Many sunscreens with SPF values from 2 through 30 are currently available with very little, if any, instructions as to which SPF number to use, when to use it, or when to reapply it.
While SPF numbers are determined in the laboratory, the actual protection factors a given agent provides in daily use varies with the user's complexion, frequency and thickness of application, perspiration and exposure to water. Hence, protection is at best a hit or miss gamble.
As the dangers of UV radiation exposure increase with the depletion of the Ozone layer (Ted Koppel, Michael Oppenheimer, Ph.D., Kevin Fay, Irving Mintzer, et al: ABC News NIGHTLINE, Aug. 26, 1987 show No. 1632, 7 West 66th Street, New York, NY 10023) and the ever-increasing need to be a sunseeking society (Robert S. Stern, M.D., Milton C. Weinstein, Ph.D., Stuart G. Baker, ScD: Arch Dermatol, 1986; 122:537-545), there is no inexpensive, readily available device that can both warn of danger and indicate what precautions to take. Aside from becomming a sun-avoidance society, the only choices are to take the gamble or stay indoors to avoid the sun altogether.